Assessment Methods

Data collation and quality control

The biodiversity assessment required sourcing and collating the best information on all known species within the priority taxa. This includes collecting information on

  • Species classification
  • Geographic range (including a distribution map)
  • Red List Category and Criteria
  • Population information
  • Habitat preferences
  • Major threats
  • Conservation measures
  • Species Utilisation
  • Other General Information
  • Key literature references

The information collated was used to assess the extinction risk of each species according to the IUCN Red List Categories and Criteria: Version 3.1. All information was then peer reviewed, where each species assessment was evaluated by at least two independent experts to ensure that: i) the information presented is both complete and correct, and ii) the Red List assessment has been completed correctly.

Regional assessments

The IUCN Red List Categories and Criteria were developed for classifying species at high risk of global extinction, i.e. for assessment at a global level. For the purposes of regional conservation assessments there are important reasons to assess species extinction risk and publish Red Lists within specific geographically defined areas. As a consequence, the Guidelines for Application of IUCN Red List Criteria at Regional Levels: Version 3.0 were used to assess the regional extinction risk for any projects looking at a restricted geographical area.

IUCN Red List Categories at the Regional Scale

The following settings and filters are also applied to regional Red List assessments:

1) Any species having less than 5% of its range within the region should not be assessed, the main assessment being completed for the neighbouring region.
2) Species present in the region prior to 1800 were treated as being “naturalised” and subject to a Red List assessment. Those species arriving in southern Africa post 1800 were not assessed but their distributions were mapped where possible.

A regional as opposed to a global species Red List Category is indicated in the text by the superscript RG following the Category assigned. For example, a species assessed as regionally Vulnerable is documented as VURG.

Species mapping

River basins were selected as the spatial unit for mapping and analysing species distributions as it is generally accepted that the river/lake basin or catchment is the most appropriate management unit for inland waters.

For the fishes, odonates and crabs, point localities (the exact latitude and longitude where the species was recorded) were used to identify which sub-basins are known to contain the species. These point localities were based on museum records from all major collections, supplemented in a small number of cases by expert knowledge of presence at sites where no voucher specimens were collected.

Connected sub-basins, where a species is expected to occur, although presence is not yet confirmed, are known as ‘inferred basins’. Inferred distributions were determined through a combination of expert knowledge, coarse scale distribution records and unpublished information. For the plants and molluscs the distribution maps are all for inferred basins as digitised point localities were not available.